 class ListNode {
      int val;
      ListNode next;
      ListNode() {}
      ListNode(int val) { this.val = val; }
      ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  }
public class demo1 {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if(list1==null)return list2;
        if(list2==null)return list1;

        if(list1.val<list2.val){
            list1.next=mergeTwoLists(list1.next,list2);
            return list1;
        }else{
            list2.next=mergeTwoLists(list1,list2.next);
            return list2;
        }
    }
}
